thanks and sorry

Hmm... If we are referring to material things, then saying "thanks" can be waived. If, however, if your friend has done you a favor like helping you paint your room or decorate the house or helping you in a school project, then saying "thanks" is a must. As for apologies, we should do this often no matter what.

Absolutely....the people you care that much about to spend time with etc..are the ones who deserved both these words....if they do something for you....absolutely...if you wrong them...again..absolutely!

yeah if you have a mistake you must say sorry and if your friend help you, you must say thank, so your friendship can survive for along time and all condition

I think that in any relationship, it is important to express gratitude even for the smallest things so that the other person would feel appreciated. And yes, I also think that we should say sorry especially if we know and feel that we have slighted a friend. These two are two things that can strengthen the relationship because we can make our friend feel important and not taken for granted.