Saying the right thing

Sometimes when one of my friends tells me about a problem I cannot relate to, I don't know what to say to make them feel better, or help them understand. It's just that sometimes I don't know the right thing to say, or what they want to hear. Usually I just say that "it will be okay", or "don't worry" even when sometimes I know that's not true. I believe that each person faces different difficulties, and that each difficulty has its own way to resolve. I want my friends to know that sometimes I may say, or may have said something that did not help them. Sorry.