?Ambition
It's very difficult to find 5 guys who get along. It's even more difficult to find 3 guys who have the same goals for the band. You will IMMEDIATELY notice which members of the band, if any, have the ambition. Some guys are talented enough to make it to the top and put $$$$$$ in their back pocket. Other band members are just happy making a cd once per year and playing a local show every other month.

There is no wrong or right here, unless you mix too many people with opposing views. The guy that is busting his balls to promote a band to hopefully make money and eventually get signed is not going to do well when grouped with a guy who wants to stay home with the kids and play 6 shows per year. It's extremely important that your band members are like minded. Is the band the most important thing in your life? Is the band the most important thing in every band member's life? Is everyone content with playing 4 shows per year? You need to ask these questions and address them.

Different goals can be a huge problem for bands. If I was trying out a new member for a band, there are only three main criteria for I would look for. #1 Character (if this guy is going to try to rape my mom, I probably don't want him in my band). #2 Musical Ability (if a guy can't play, there is little reason to have him in the band). #3 Similar Ambition (If the guy doesn't want the same things that I and the rest of the band want, there will be big problems later and I'd rather put a stop to them now).

Evolution
Seasons Change. People Change. I'm not sure why I'm quoting this popular late 80s / early 90s song. Either way, your views, opinions, beliefs, and experiences will be much different the day you start your band vs the day you end your band. It's impossible to predict how each member of the band will evolve, but sometimes people end up going different routes. Metal heads in high school turn into jam band guys in college. The lead singer who started being serious about being a star may be serious about his family when he gets a girl pregnant. There are a million factors in a band that can shake up the foundation of what made the band in the first place. You will never predict these. Just be aware of them. No matter how great the band is doing, there are factors that will change things in a whim.

Here's an example. Back in the day, I was 20 years old and very serious about my band. We were practicing a couple of times per week and playing miniature shows in the basement to friends every Saturday. We had to stop at 10pm on Saturdays so after that we partied. We had lots of chicks and figured out a nice system for making sure that we had beer, even though we were underage.

Well, there was an accident at work, and my step dad was killed. I handled it okay, but my mom was devastated. She was a complete wreck. Now, 6 years later, she is finally coming together. Anyway, when that all went down, my views changed. Instead of partying every Saturday night like the rest of the band, I found myself spending time with my mom quite a bit more. I have no doubt that I was making the right decisions.

However, the band wasn't so good at putting themselves in my shoes. Maybe I didn't communicate well enough with them? Either way, the fact that I wasn't spending as much time with them was clearly alienating me from the band and it eventually lead to me leaving the band.

This is just one example where evolution can have a huge impact on your bands ability to stay together.