If you're not stubborn, you'll give up on experiments too soon. And if you're not flexible, you'll pound your head against the wall and you won't see a different solution to a problem you're trying to solve.
Percentage margins don't matter. What matters always is dollar margins: the actual dollar amount. Companies are valued not on their percentage margins, but on how many dollars they actually make, and a multiple of that.
If your customer base is aging with you, then eventually you are going to become obsolete or irrelevant. You need to be constantly figuring out who are your new customers and what are you doing to stay forever young.