In his book Tribe of Mentors, Tim Ferriss details his interviews with high performers. In the interview with designer extraordinaire Debbie Millman, Debbie explains her thoughts about being busy.
Busy is a decision. Of the many excuses people use to rationalize why they can’t do something, the excuse “I am too busy” is not only the most inauthentic, it is also the laziest. We do things we want to do, period. If we say we are too busy, it is short hand for “not important enough.” It means you would rather be doing something else that you consider more important. If we use busy as an excuse for not doing something what we are really saying is that it’s not a priority. You don’t find the time to do something; you make the time to do things.
I think many people use the phrase "I'm too busy" as a polite way to get out of obligations that they simply don't want to commit to.
The problem is when you say "I'm too busy" to yourself. Most likely this is just an excuse to hide the truth. Think about the real reason why you don't want to do something. Is it something important that you really should be doing? Don't let the excuse of being too busy get in the way of accomplishing your goals.