Why are tradesmen so difficult to ask to stick to timings?

Trades rarely run to a perfect schedule because the work is hands-on, variable, and often depends on factors outside the tradesperson's control. A few of the main reasons: Hidden problems Once someone starts taking things apart, they often find issues nobody could see during the quote stage, such as rotten joists, corroded pipes, unsafe wiring, or bad previous work. Fixing these adds time. Reliance on suppliers Materials go out of stock, deliveries run late, or the wrong items turn up. A lot of jobs stall simply because the needed parts are not on site when expected. Customer changes People often change their minds mid-job. Even small tweaks can add hours or days, which then pushes everything else back. Knock-on effects Most tradespeople juggle several jobs at once. When one job overruns for any reason, it pushes the schedule for the next one. Weather and site conditions For outdoor or structural work, bad weather or an unsafe site can halt progress completely. Unpredictable complexity No two homes are identical. Older homes, especially, can behave in ways that nobody can fully predict until the work begins. In short, trade schedules slip because real-world conditions are messy. It is not usually laziness or poor planning; it is simply the nature of working with buildings, materials, and variables that cannot be controlled perfectly. Here is a real-world example. We ordered a full house of radiators, a toilet, a kitchen sink, and the unit. These were ordered as soon as the customer accepted the quote on the 12th. Everything arrived apart from the kitchen sink and the unit. These were delayed in transit. The order was placed on the 12th of November, and the sink unit did not arrive until the 26th. By that point, everything else in the house was finished. I had to reshuffle the entire month's calendar just to return and complete that one part of the job. I even built plenty of space between jobs to deal with unforeseen issues, but delays like this still cause disruption. Even travel can be a problem. It recently took two hours to go ten miles because of unexpected roadworks. This is the reality of why schedules slip, even with good planning.