Simple math dictates that the more tasks you take on, the less effectively or successfully you'll be able to do any one of those tasks individually. You are a finite being. Meaning, there's only so much time, energy and brain power to go around. Stretch yourself long enough or far enough and, like a piece of gum, you'll start seeing holes.
You've, no doubt, heard the phrase: "Jack of all trades, master of none"...and it's true. While this can be a positive thing if you're, say, a maintenance man or a personal assistant, it's not so good if you're trying to make a lasting mark on this world. Adding things to your plate will only diminish the effectiveness with which you can complete the other things that are already there. In time, you'll become 'pretty good' or 'pretty effective' at a lot of stuff, but not 'really good' or 'really effective' at anything.
Whether it's at work, at home, at church, or at school, people gravitate to remarkable. To outstanding. Not to mediocre or to average.
Have you been stretched to the point of mediocrity?