Easy, Moderate, and Hard to grow strains

Different seedbanks have different degrees of difficulty for the same strain.

What is the difference in difficulty? Comparing something like a silver haze to a skunk, there is a huge difference on the websites but Im curious how different.

What makes an easy grower different from a hard to grow strain and why?

If anyone has the time, please try to be specific if possible.

Peace, Rance

im interested in this to because i was going to try to grow bluebarry but was told its a 'hard' strain to grow because of its sensitivity to nutes and ph.