You've just finished slicing raw meat and now you go to rinse the knife. Turning on the hot water, you let the water gush over the blade to rinse away the streaks of fat that have accumulated there. After a moment, you have to grab the scrubby sponge you keep at the edge of the sink to remove the more determined bits that refuse to come off. What's happening there?
You're essentially cooking the fat and bits of flesh that are still on the knife. When the proteins are exposed to hot water, they tighten up, shrinking and adhering to the metal surface. In other words, you're better off rinsing the knife with cold water for ease of cleaning. Once you've removed the goop, you can switch to hot water to finish cleaning the blade.
Assuming you rinse your knife in this manner at least five times a week, in a process that takes about 45 seconds, you've saved yourself 117 hours over a lifetime of cooking.
You don't have to thank me.