Why should my measuring stick prevent me from being able to divide a 1 meter length of wood into 3rds? Sure, they use millimeters....but this is an unfortunate

Why should my measuring stick prevent me from being able to divide a 1 meter length of wood into 3rds? Sure, they use millimeters....but this is an unfortunate workaround for a defect of the metric system. The proof is that if you look at the number of millimeters in the specified length, more often than not its something like 1,200 millimeters, viz, a number which is really big and divisible by 3.