If you've ever picked a weight-training exercise and attempted to increase your personal best, you know that instinctively you want to lift as much weight as you can almost every time you do it. I know I do, and have since I first started lifting in high school. After all, who wouldn't like to say they increase their bench press max every week by 5-10 pounds? The younger and less experienced you are, the more you can get away with this method and the more it will seem to work. But as you get better and older, and especially as you get into more technical lifts like the Olympic lifts, this method starts to fail. After doing the same amounts each week, your lifts will plateau or, worse, start to decrease. Your technique tends to get worse because, well, it's HARD to have good technique at maximum weight! If you watch the top Olympians lift, you'll see they keep amazing form even at world-record weights. Which is, of course, the reason they can lift world-record weights, not to mention they're strong as hell.
What does this mean and how does it relate to training? It means that a good workout is tailored to give the lifter lots of opportunities to lift somewhat lighter weights that train his or her technique and prepares them for days where they get to lift at or near maximum. When done right, the lifter gets enough rest, doesn't injure themselves, and keeps improving technique and strength. It's true that your personal bests might not increase as fast as you want, but since when do you get what you want simply because you want it? I've seen plenty of people lift beyond what they can do correctly every day, and it isn't pretty. How many times in a row can you miss snatching the same weight before it starts to make your technique worse? And, worse yet, training at the edge of your ability all the time almost invariably causes injury.
As a lifter, you (and, if you have one, your coach) has a responsibility to make sure you don't fall prey to this peril. Set limits for yourself BEFORE your workout as to how heavy you will go in an exercise. If your form starts to fail you, stay at a weight where you can do it correctly, and maybe do extra reps. You will still get stronger without lifting at the top of your range. Then you might just surprise yourself on your heavy day when suddenly you can add 5kg-10kg to your old max.
I admit, this is a problem of mine, too. But sometimes I can do it right. It's alright that I didn't get any PRs over a week span - I wasn't supposed to. But it's certainly interesting to note that I've begun cleaning and jerking 140kg regularly, and I can't remember the last time I missed one. We'll see how that translates in the next two meets I have scheduled: the East Coast Classic in Moorestown, NJ on April 26th and the Maryland State/Potomac Valley Championships at Fort Detrick in Frederick, MD on May 10th. I only need 247kg for Senior Nationals next year, and I did 108kg in the snatch and 142kg in the clean and jerk just the other week....