It basically means, be extra careful before you cut, so you get it right the first time.
Today I invented a new version of that time-tested cliche: Measure twice, cut twice. Basically, it means measure twice, but leave enough of a margin for error, so that if you have to cut twice, you're able to do so.
Luckily, I was able to. We spent the last couple of days making round-bottom coopering planes. These are more complicated than the planes we've previously made, and are used to make curved doors, which are pretty much the coolest thing ever.
Once mine was cut, laid out, glued up and ready to go, I sketched out a shape that a liked and headed into the machine shop to cut it out. I even showed it to my benchmate Jim and a friend Max, and they both liked it.
I cut it out on the band saw and walked back to my bench feeling pretty awesome about it, when I suddenly realized it was backwards. I had completely reversed it, and the plane's shape suddenly made no sense at all.
I quickly put it under my bench and sat down, feeling miserable. Jim took one look at me and said 'where's your plane??' thinking I had thrown it in the trash.
I pulled it out and showed it to him, and he studied it for a minute before breaking out laughing. He's normally a pretty polite guy, but couldn't control it. I don't blame him, I busted out too, and pretty soon a group had gathered around, all laughing at my mistake.
Then Laura, our instructor and the director of the program, came over asking to see me 'Canadian pull plane,' had a good laugh and quickly showed me how I could fix it.
In the end, all was well because I had enough material to change the shape and reverse the direction -- essentially, to fix my mistake. The lesson: Measure twice, cut twice.
Or better yet, learn from my mistake and get it right the first time.