It's the simple things that open the heart. Lovely photograph, Maggie. Why is it's for it is wrong grammar, by the way, I thought that was OK?
Yikes! 'Send' was hit by accident, before morning coffee!
The answer is that 'is' is singular, and 'things' is plural. A correct sentence would be something like: some of the things in life that are most pleasing ARE [they are].
Gotcha – I didn't pick that up at all! But if it feels all right then maybe it is all right. I do have pet hates – for instance when someone says the phenomena/criteria is, because it's posh-sounding but just plain wrong. However, when my Mum picked up my son for saying "them things" I just told her that was how it was expressed in Sunderland….