Is it normal i can't take the first one

I will always take the second one. For example, when shopping I never take the first one on the shelf, I take the one behind, regardless of date. In unopened packets of things like cheese slices or biscuits, I can't take the first one, I wait until someone else takes it. I have been forced to eat the first in a packet before and it makes me feel sick. This has started to extend to non food things too.