Excess surrounds us on a daily basis and after a while it ends up being the norm. Getting a "super sized" meal or an "xtra larger" drink is almost a reflex. The tendency to do too much doens't limit itself to consuming calories. If you are trying to make strength gains the biggest mistake you can do is to try and do more than you need - but that's exactly what most people will do. The mentality that "if a little is good then more is better" doesn't apply when it comes to strength and conditioning.
More isn't better - it's just more; and it can actually it keeps you from making progress. Trying to PR your Deadlift before you put in the requisite preparation is just asking for an injury. Attempting Jerks before you have gotten a good handle on your Military Press and Push Press is downright stupid. But people will push harder and longer in the hope of getting better results (or a better score on a WOD)... when the real key to success is not working harder but working smarter (and putting in the time i.e., consistency!)
Doing too much work is almost as bad as doing too much of one thing. Focusing on one thing at the expense of not doing a balance of work is asking for trouble. Focusing on your Squat and Pull Ups and not doing any Mobility work or anaerobic conditioning is going to leave some holes in your athletic ability. Any combination that focuses too much on one aspect is not a good idea - unless you are training for a competition that requires that skill; then have at it and fix the imbalances later!