I have put together a puzzle or two in my life. I don't think I ever actually start one, but I always stop and help someone else with theirs. I can still remember my parents rules if we were working on a puzzle together. "Always start with the edges! Corners first!" Now let's be honest, if there are a thousand puzzle pieces on a table and all of them are the size of a toddlers fingernail then finding the four corners can take a while!
My three preschoolers and I were visiting at my parent's house recently, and I watched as my mom tried to enforce these same rules with my kids. I made sure my snickers weren't audible. My three year old would lose interest rather quickly and just leave. My 4 year old daughter understood perfectly, but you can't tell her anything right now. She has to do it her way. While she is very analytical and does well with the puzzles, its slow progress because she has to use trial and error instead of your help.
On the other side of the table, I could see my four year old son's confusion at the concept of flat sides and corners. He's used to the pieces you slide around on the wooden frame until they accidentally pop in place. Once my mom helped him with the outside pieces, he decided he would do the rest of the 30 piece Spiderman puzzle on his own...without help. Saying that to his sister, as nosy and bosssy as she is, is like throwing gasoline on a fire. When he says, "Don't help me", she automatically starts creeping over next to him. As soon as he looks down she starts instructing him as to how he should be doing it. "I said leave me ALONE!" Once I make her leave the table completely I watch my son put his puzzle together with his Mammaw (who is "not" helping). She hands him a piece to "try". Now my mom and I could both see that the piece needed to be turned just a little. My son lays it down and starts beating it with his fist, trying to force it in. I think my mom picked the puzzles up for a few years.
Since we're talking about puzzles (most likely against your will), have you ever watched someone work on a puzzle? It is the dullest thing...EVER! Why? They are doing it too slow.That piece doesn't go there. You're doing it the wrong way. Bottom line, it's because we aren't in control.