Claim
What a tailor can change easily
Routine, cheap and quick: shortening sleeves, shortening trousers and choosing your break, taking in a waist on trousers or a jacket, tapering trouser legs, shortening a shirt, slimming shirt sides, moving a button, replacing a lining.
Harder and more expensive but usually possible: shortening a jacket body, narrowing lapels, reshaping a shoulder slightly. Rarely worth it: widening anything beyond the seam allowance, which is the spare fabric left inside a seam, because there is only a few centimeters of it and once it is used the garment cannot go out again.
Evidence
What cannot be changed, and why
Three things are effectively fixed. Shoulder width, for the sleeve head reason from day 1. Armhole height, because raising it means recutting the body and the sleeve together. And overall length in most casual garments where there is no hem allowance to let down.
This is the practical reason day 1 ranks the checkpoints in that order. Buy for the things that cannot change, then alter the things that can. Applied to shopping, it means trying a size up for the shoulders and chest and having everything else brought in, which is what men who look well dressed in off the peg clothes are almost always doing.
Action
Take one garment in this week
From your day 1 alterable pile, pick the item you would wear most if it fitted. One item, not five.
Wear it to the tailor, put on the shoes you wear with it, and ask them what they would do. Then ask for the price before agreeing. Expect trouser hems and sleeve shortening to be inexpensive, jacket waist work to be moderate, and anything involving the shoulders to be quoted high enough that you will decline. Collect it, wear it for a week, and then decide whether to bring the next two.
Claim
How to talk to a tailor
You do not need vocabulary. You need to describe the problem and let them name the solution, because that is their job and they are better at it than you.
Three sentences: here is the item, here is what bothers me about how it sits, what would you do. Then listen to what they refuse. A good tailor will tell you when an alteration is not worth the money or will not achieve what you want, and that refusal is the strongest signal you will get about whether to use them again. Bring the right shoes for anything involving trouser length, or you will be guessing.
Example
Robert had a charcoal suit from a wedding that he described as boxy and never wore. Total alteration cost was 48: trousers taken in at the waist and tapered below the knee, jacket waist brought in by two centimeters, sleeves shortened by two.
He wore it eleven times in the following three months, including to two interviews. The suit had cost 210 four years earlier and had been worn twice. What he actually bought for 48 was a suit he already owned, which is the best return on any clothing money in this course and the reason this day exists at all.
Caution
The over-altered garment
Alterations have a limit and pushing past it produces a garment that is wrong in a new way: pockets pulled out of position by a waist taken in too far, a jacket shortened until the proportions no longer make sense, trousers tapered so narrowly that the hem cannot pass over the shoe.
As a rule, two or three interventions on one garment is sensible and five is a rebuild. If a tailor tells you an item needs five, the honest answer is that it was the wrong garment. Thank them, pay for nothing, and remember the shape of that mistake the next time you are in a shop with a jacket that is nearly right.
Aside
Made to measure, and whether it is worth it
The obvious next question is whether to skip alterations and have things made. Made to measure means an existing pattern adjusted to your measurements. Bespoke means a pattern cut for you from scratch, usually with fittings, and it costs several times more.
For most men, off the peg plus a good tailor gets to roughly 90% of the fit of made to measure for a small fraction of the price, and the remaining 10% matters mostly if your proportions are far from the pattern the industry cuts for: very tall, very short, strongly built across the chest, one shoulder noticeably lower. If that is you, made to measure is not a luxury, it is the only route to the fit day 1 describes. If it is not you, the tailor is the better spend.