To often the "burden" of ministry is relayed in low pay, long hours, unappreciative people, etc. The reality is perhaps far more personal for many and the occasional reality for all. Spurgeon described is succinctly as the Pastor and His Fainting Fits.
Our work, when earnestly undertaken, lays us open to attacks in the direction of depression. Who can bear the weight of souls without sometimes sinking to the dust? … To see the hopeful turn aside, the godly grow cold, professors abusing their privileges, and sinners waxing more bold in sin—are not these sights enough to crush us to the earth?
How can we be otherwise than sorrowful, while men believe not our report, and the divine arm is not revealed? All mental work tends to weary and to depress, for much study is a weariness of the flesh; but ours is more than mental work—it is heart work, the labour of our inmost soul. How often, on Lord's-day evenings, do we feel as if life were completely washed out of us! After pouring out our souls over our congregations, we feel like empty earthen pitchers which a child might break. Probably, if we were more like Paul, and watched for souls at a nobler rate, we should know more of what it is to be eaten up by the zeal of the Lord's house. It is our duty and our privilege to exhaust our lives for Jesus. We are not to be living specimens of men in fine preservation, but living sacrifices, whose lot is to be consumed; we are to spend and to be spent, not to lay ourselves up in lavender, and nurse our flesh. Such soul-travail as that of a faithful minister will bring on occasional seasons of exhaustion, when heart and flesh will fail. Moses' hands grew heavy in intercession, and Paul cried out, "Who is sufficient for these things?" Even John the Baptist is thought to have had his fainting fits, and the apostles were once amazed, and were sore afraid.
Our position in the church will also conduce to this. A minister fully equipped for his work, will usually be a spirit by himself, above, beyond, and apart from others. The most loving of his people cannot enter into his peculiar thoughts, cares, and temptations.
The lesson of wisdom is, be not dismayed by soul-trouble. Count it no strange thing, but a part of ordinary ministerial experience. Should the power of depression be more than ordinary, think not that all is over with your usefulness. Cast not away your confidence, for it hath great recompense of reward. Even if the enemy's foot be on your neck, expect to rise and overthrow him. Cast the burden of the present, along with the sin of the past and the fear of the future, upon the Lord, who forsaketh not his saints. Live by the day—ay, by the hour. Put no trust in frames and feelings. Care more for a grain of faith than a ton of excitement. Trust in God alone, and lean not on the reeds of human help. Be not surprised when friends fail you: it is a failing world. Never count upon immutability in man: inconstancy you may reckon upon without fear of disappointment. The disciples of Jesus forsook him; be not amazed if your adherents wander away to other teachers: as they were not your all when with you, all is not gone from you with their departure. Serve God with all your might while the candle is burning, and then when it goes out for a season, you will have the less to regret. Be content to be nothing, for that is what you are. When your own emptiness is painfully forced upon your consciousness, chide yourself that you ever dreamed of being full, except in the Lord. Set small store by present rewards; be grateful for earnests by the way, but look for the recompensing joy hereafter. Continue, with double earnestness to serve your Lord when no visible result is before you. Any simpleton can follow the narrow path in the light: faith's rare wisdom enables us to march on in the dark with infallible accuracy, since she places her hand in that of her Great Guide. Between this and heaven there may be rougher weather yet, but it is all provided for by our covenant Head. In nothing let us be turned aside from the path which the divine call has urged us to pursue. Come fair or come foul, the pulpit is our watch-tower, and the ministry our warfare; be it ours, when we cannot see the face of our God, to trust under the shadow of his wings..
 Spurgeon, C. H. (1875). Lectures to my students: a selection from addresses delivered to the students of the Pastors' College, Metropolitan Tabernacle. (Vol. 1, pp. 178–179). London: Passmore and Alabaster.
 Spurgeon, C. H. (1875). Lectures to my students: a selection from addresses delivered to the students of the Pastors' College, Metropolitan Tabernacle. (Vol. 1, pp. 170–173). London: Passmore and Alabaster.
To pray successfully is the first lesson the preacher must learn if he is to preach fruitfully; yet prayer is the hardest thing he will ever be called upon to do and, being human, it is the one act he will be tempted to do less frequently than any other. He must set his heart to conquer by prayer, and that will mean that he must first conquer his own flesh, for it is the flesh that hinders prayer always.
Almost anything associated with the ministry may be learned with an average amount of intelligent application. It is not hard to preach or manage church affairs or pay a social call; weddings and funerals may be conducted smoothly with a little help from Emily Post and the Minister's Manual. Sermon making can be learned as easily as shoemaking—introduction, conclusion and all. And so with the whole work of the ministry as it is carried on in the average church today.
But prayer—that is another matter. There Mrs. Post is helpless and the Minister's Manual can offer no assistance. There the lonely man of God must wrestle it out alone, sometimes in fastings and tears and weariness untold. There every man must be an original, for true prayer cannot be imitated nor can it be learned from someone else. Everyone must pray as if he alone could pray, and his approach must be individual and independent; independent, that is, of everyone but the Holy Spirit.
Thomas à Kempis says that the man of God ought to be more at home in his prayer chamber than before the public. It is not too much to say that the preacher who loves to be before the public is hardly prepared spiritually to be before them. Right praying may easily make a man hesitant to appear before an audience. The man who is really at home in the presence of God will find himself caught in a kind of inward contradiction. He is likely to feel his responsibility so keenly that he would rather do almost anything than face an audience; and yet the pressure upon his spirit may be so great that wild horses could not drag him away from his pulpit.
No man should stand before an audience who has not first stood before God. Many hours of communion should precede one hour in the pulpit. The prayer chamber should be more familiar than the public platform. Prayer should be continuous, preaching but intermittent.
It is significant that the schools teach everything about preaching except the important part, praying. For this weakness the schools are not to be blamed, for the reason that prayer cannot be taught; it can only be done. The best any school or any book (or any article) can do is to recommend prayer and exhort to its practice. Praying itself must be the work of the individual. That it is the one religious work which gets done with the least enthusiasm cannot but be one of the tragedies of our times.
Tozer, A. W., & Bailey, A. M. (1992). God tells the man who cares (pp. 63–64). Camp Hill, PA.: WingSpread.