Too many people confuse "bench press" with strength of character and moral virtue.

Fragility is the danger.  The priesthood requires too much self gift for men who aren't mature enough and are fragile.

Virtues are "strengths", dispositions to do the good and the hard and the noble.

Priests need to be always working on their manly virtues. The self-focused ones, the ones given to sensuality and other disorders put themselves into risk.