I tell myself that every little bit helps, ask myself, would I rather have lost that half pound (or less) this week? or gained it, because it is so small and insignificant?
Generally I find I'm glad to have lost even the tiniest amount of weight. Several weeks of .5 lb or less accumulates into five or ten pounds every couple months.
Edit***
Um, I guess that wasn't really what you were talking about. The topic is about being patient, not frustration with tiny increments of loss. My bad.
As far as the actual topic goes: when I get weary of how looooooong I know it's going to take to lose the 100 lbs I still have to get off my frame, I remember a (former) friend of mine. I met her when she was in her thirties and she was slim, but not healthy... that is, not huge, but not toned or supple or particularly well-nourished-looking, I think I've heard it called "skinny-fat." She told me many many times that in her late twenties, she was bigger than I was and that after having her baby at age 26, she cracked down and lost all the weight (about 95 lbs) in about six months. She never said so, but I wouldn't be surprised to learn there was another kind of "crack"ing down going on. Losing the weight so fast and in such an unhealthy manner left her body looking deflated, and at age 33, she had the body of a 50 y/o who'd been ridden hard and put up wet.
My point being, when I get a little daunted by the enormity of the task, I remember that slow and steady gives my body it's best chance to look it's best when the journey is done. If I lose it all too fast with crash diets and pills and insisting on losing six lbs/week, I risk loose, hangy skin where I don't want it, and I DON'T WANT THAT.