Part of the issue of achievement is to be able to set realistic goals, but that's one of the hardest things to do because you don't always know exactly where you're going, and you shouldn't.

Lucas frames “achievement” less as a single triumph than as an ongoing practice of navigation: you need goals to orient effort, yet the future is inherently uncertain and, in creative life, should remain partly open. The paradox—set realistic goals while admitting you can’t fully know where you’re going—suggests a balance between discipline and discovery. The final clause (“and you shouldn’t”) implies that over-determining outcomes can narrow experimentation, making success less likely in fields where innovation depends on surprise, iteration, and learning from failure. The quote thus endorses flexible ambition: aim concretely, but leave room for the path to change you.