Very simple PF question: AJo

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Although new to internet poker (I occasionally play on my friend's account at PP $25NL), I still feel that internet poker isn't THAT much different than live.

My buddy (who is far less experienced, doesn't play half as much as I, nor reads anything and plays seldom) had AJo in the BB. This is PP $25. An EP raised and everyone folded to him. EP is unknown with 100BBs.

I recommended fold. He told me we probobly wouldn't see a hand as good as that for a while. I attempted to explain the gap concept from TOP and found that I had difficulty explaining the concept. Can anyone give a fairly good, simple explanation?