The decision usually arrives from exhaustion. There is more work than hours, evenings are being used to catch up, and turning jobs away has started to feel routine. Hiring looks like the obvious answer, and often it is - but the first person changes the business more fundamentally than the second or the tenth, because it forces everything held in one head to become explicit.
The first surprise is how much that turns out to be. Which supplier for which material and why; what to say when a customer asks for something slightly outside the usual; how a job is priced; what good enough looks like; which corners are acceptable when running late and which are never. None of this exists in writing. It has been accumulated over years and applied without conscious thought, and a new person cannot absorb it by being nearby. Businesses that find the first hire disappointing have often hired a capable person and given them no way to learn the things that actually matter.
This is why the first weeks feel like a loss. Output goes down, because the experienced person is explaining rather than doing, and the new person is slow because they are learning. That dip is normal and temporary, but it is genuinely a dip, and a business that hires at the exact moment it is most overloaded can find the extra load arrives before the relief does. Hiring slightly earlier than feels necessary is easier than hiring at the point of crisis.
The practical preparation is to write things down before the person starts rather than during. Not a manual - a handful of pages covering the routine jobs step by step, the prices, the suppliers, and the decisions that come up weekly. It takes a few evenings, it is dull, and it converts the first month from continuous interruption into something closer to independent work. It also has a second use, since the same pages are what let you take a week off later without the business stopping.
The obligations are the part most often underestimated. Employing someone brings contracts, payroll, tax, insurance and a set of legal duties that vary by country and are not optional, and the cost is meaningfully higher than the wage itself. This is worth working out precisely before committing, with proper advice, because the figure decides whether the hire is affordable - and it is far better to discover the real number while it is still a plan than after somebody has given notice at another job.