Locknut:
Every trade in the home center (carpentry, wiring, plumbing, etc.) has some science to it, just as paint does (and all coatings do).
The difference with paint is that it's not being taught anywhere like other trades are, and it's the resulting knowledge vaccuum that produces fertile ground for misunderstanding and misconceptions to take hold and spread. Typically, we turn to the people mixing the paint in the home center for advice on what paint to use where, and they don't know themselves. About the only "experts" they have to turn to are the sales reps that stock their shelves, and they know precious little and then only about the paints their company makes. It's very much a "blind leading the blind" situation.
You can learn more than you need or want to know about latex paints at:
Paint Information, Decorating with Paints, Paint Trends - Paint Quality Institute
This is the web site of the Paint Quality Institute, which was established and is funded by the Rohm & Haas Company who are the largest manufacturer of the plastic polymethyl methacrylate (also called "Plexiglas") in North America. Most people are unaware that quality paint is also made from tiny particles of polymethyl methacrylate (or Plexiglas) which fuse together to form a continuous film of plastic during the film formation process. Nothing about oil based or latex paints is hard to remember or difficult to understand. It's just that it's not being taught anywhere, so people don't know anything about it, and misconceptions and misinformation run rampant.
PS: You don't need to know the rest:
An example of a modern day misunderstanding about paint:
That word "enamel" as it applies to paint almost certainly originated when someone tinted a can of varnish in a paint tinting machine. Years ago, varnish only came in semi-gloss and gloss. Also, varnish, like the linseed oil based paints of the time, used dried plant resins (called "copals") to impart better hardness and durability in the varnish (or paint). The difference was that varnishes would use more of the best quality copals, which were the ones that imparted the most hardness and durability while affecting the colour of the coating the least. Consequently, if you tinted a can of varnish to make a real "enamel", the paint you got would be semigloss or gloss and would dry to a harder and more durable film than regular paint. So the word "enamel" came to mean a paint that would dry to a harder and glossier film than you'd otherwise expect.
In 1956, the Bayer Company (the Aspirin people) patented the very first urethane modified alkyd resin by adding something called polyisocyanates to the pot while making the alkyd resins. This caused urethane groups to form within the alkyd resins. Urethane groups are very strong, and they acted much like the roll cage inside a race car, making that alkyd resins harder if you tried to crush it and stronger if you tried to stretch it. The result was a harder and more durable clear coating for wood, and "polyurethane" soon replaced varnish as the clear coating of choice over wood. Since polyurethane has replaced varnish as the clear coating of choice over wood, you'd make a modern day "enamel" by tinting a can of polyurethane hardwood floor finish in a paint tinting machine to make "enamel" paint. And, those paints ARE made. They're called polyurethane floor paints, and they're quite common.
But, because of continual improvements in the binders, rheology modifiers and other additives used in paints, EVERY paint dries to a harder and smoother film than the same paint did a decade or two ago (save for the dead flat paints), so EVERY paint can be argued to be an "enamel" cuz it dries to a harder smoother film than you'd expect if the last time you used it was in 1968. And, now, some companies (like Behr) have come to calling every dam paint they make an "Acrylic Enamel". In this case, the meaning of the word "enamel" changes slightly to: "Hey you. Yeah, you. Buy me." The truth is that the paint in the can is no different than any competitor's "paint". It's just that the word "enamel" is being used as a racing stripe to suggest to the consumer that it's a better paint (cuz it's an "enamel").
Have fun with it. Take the tinted Behr eggshell back for a refund because it says "enamel" on the label, but it's really just ordinary paint inside, and so there musta been a mix-up at the factory. Or, demand to test the "enamel" against a normal "paint" before you buy it to make sure it really is an enamel (cuz the last time you bought "enamel" it turned out to be ordinary paint). Be creative, and have fun.