Of course there are no guarantees, and of course we're talking about psychology here. It's "mental health", not "rigorous planning". I'm also an engineer; in fact I teach engineering to college students. We sling equations for a living. It's all about stating one's assumptions, drawing a diagram, finding the correct mathematical model, solving the problem, plotting the solution, then confirming that it makes sense. Nowhere in that process do we mention feelings, because engineering is about doing applied-physics. Feelings don't build airplanes. Feelings don't keep hydroelectric dams functioning. Feelings don't prevent bridges from collapsing. But feelings are exactly what we talk about, when we talk about "mental health". It isn't about my wealth, but how I feel about it. It isn't about meeting my expenses, but how I feel about potential scenarios.
Fear isn't an ingredient in the decision-making process. Math is. But math isn't an ingredient in our mental-state; fear is. Fear is by its very nature irrational. Nowise does something have to happen, for me to fear it! Inversely, I might not fear something highly likely and devastatingly harmful... maybe because I'm a big hero, or just in denial.
The real key to our mental health isn't about good planning, self-control, maximizing our potential, working hard, being a decent person and so on. These all doubtless assist our progress and our practical success. But mental health isn't about being successful. It's about feeling successful. The junky in the gutter might be feeling successful, having no reason to do so. The billionaire on his private island might be feeling unsuccessful, having no reason to do so.