Measuring calories: Why is it so damn hard?

I'm using SparkPeople to keep a food journal. I'm wondering how accurate it is. The product information is correct as far as I can tell, but I'm nervous about unpackaged food portion size. Did I eat 3 tablespoons of balsamic vinaigrette dressing? How many red beans were in my salad, a fourth of a cup or a half a cup? I'm not sure. I actually feel like it was less than that, but I don't want to under report. Anyway, I don't want to get to obsessive about this. Journaling should just be used as a guideline. It's best to be used as a tool for conscious eating--awareness. I've always found it to be necessary for me to lose weight, and experts do point to it as a necessity.

Let's be honest. It's joyless and tedious. It takes out a lot of the joy of eating. At best it appeals to the geekier side of me. I can never keep it up for longer than a month. I'm determined this time around to be more consistent.