Superconductivity. I did four PhD projects regarding superconductivity properties at nanoscale without really getting hold on the concept. For instance, how zero resistance is related to cooper pair tunnelling and BdG Hamiltonian. Only when I was forced to write introduction a month before my thesis submission I gave my best last try for the farewell and it clicked. Note the title of my thesis “Quantum effects of superconducting phase” ;)

Quantum computers. I was so deceived by all the hype that it took me long to see it as SU(N) matrix product accelerator.

Zero knowledge proofs and Shamir transform to non-interactive protocol. The tunnel analogy did quite a harm to me, also the math was just unbearable (defining set of languages and etc). Only a year ago when I got an old paper on “Observational wallets” describing how to prove ‘log_g A = a’ and ‘log_g A = log_g B’ the whole ‘proving statement without revealing secret’ after long frustration and angst made sense to me. If I had encountered finding Vodo analogy first, It would have clicked much quicker to me.