However or yet

I always get confused between “Yet” and “However”. Please help me.

For example, These are some of the expectations they have. However/Yet, many of them do not know how to meet them.

Let me make an attempt with some modifications so as to make it more understandable.

These are some of the expectations they have. (Supposing that they are great expectations). However, I’m sure I can meet at least one of them.

These are some of the expectations they have. (Supposing that they are small expectations). Yet I’m not sure if I can meet at least one of them.

He is poor. However, he never seeks help from others.
He is poor. Yet, he always tries to help others.

(It, therefore, follows that we are able to use these linking words only on the basis of the ideas to be expressed)