Learn English – Suitable saying for “different people like/dislike different things”

2 sentences that comes to my mind are:

Physician, heal yourself! 1

and

The shoemaker's children go barefoot 2

Both are referring to people who are able to help others, but have problems help themselves. Although the situation is a bit other, because in your case the person that have helped you got the same problem not in the same time, but afterwards.

Disclaimer while in first case I'm sure it has the same meaning as in my languange, in second case in Polish the saying is referring to the shoemaker going barefoot himself.

It may pertain to the maxim "the worse, the better", often attributed to Vladimir Lenin in the years before the Communist Revolution.

There is a related philosophical idea: the modern (Hegelian/Marxist) use of the term dialectic. Hegel's idea was that each concept or position, theoretical as well as practical, continues to develope until it becomes useless and corrupt - entangled in its own contradictions. Then, a shift is made to another concept/position - the negation of the previous concept/position. Marx used the same idea in economical and political contexts. Hence the famous prediction concerning the imminent collapse of capitalistic economies, destined to be caught up in their own contradictions, until there is no remedy but a popular workers revolution.