Gardening.

As an engineer I like to imagine I can build and the structure stays up like a stone arch.

But a person and even a habit is not stone or silicon but living. So what does it even mean to "work on" something which is living?

Gardening

You absolutely _can_ build terraces and trellises. And self-help books can give you great seeds and saplings.

Yet there will always be watering and weeding to be done.

If you want your life to bear the fruit of your choice, it is up to you to rise every morning and tend to your garden.