Skill Composition
Skill composition is a funny thing. On the one hand, a team without the right composition of skills at the right level is going to cause problems. On the other hand, most leaders tend to hope their team can figure that out by themselves.
Some of this can be due to budget, some can be due to aggressive schedules that don't allow for training and skill development.
Either way, great teams have the right composition of skills at the right level, and you pay in quality and loss time without it.