What Contributes the Most to a Team's Success?

[Koko Ed]

While all of these answers combined make a strong team my question is which aspect most contributes to a team's success.
I'll go with experienced mentors. The students are a variable. At the most they can stay four years (six if you take them in middle school and in rare cases they have been around even longer) but veteran mentors who stay with the team year after year after year are the ones who keep the fire going. And even after they have graduated many of the students become those mentors who take the lead (which is partially what Dean wanted. Take what you have learned and pass it on to the nest generation). The other things are nice and all but team can and have lived without them. Without good mentors teams don't last long.