  We perform a systematic study of the $\alpha$-particle excitation from its
ground state $0_1^+$ to the $0_2^+$ resonance. The so-called monopole
transition form factor is investigated via an electron scattering experiment in
a broad $Q^2$-range (from $0.5$ to $5.0$ fm$^{-2}$). The precision of the new
data dramatically superseeds that of older sets of data, each covering only a
portion of the $Q^2$-range. The new data allow the determination of two
coefficients in a low-momentum expansion leading to a new puzzle. By
confronting experiment to state-of-the-art theoretical calculations we observe
that modern nuclear forces, including those derived within chiral effective
field theory which are well tested on a variety of observables, fail to
reproduce the excitation of the $\alpha$-particle.
