"If you are any good at basic mathematics,"

I tell her, "You could take one row of hearts out and then knit the border."
The would-be knitter of the shawl looks at me as if I have gone mad. Fortunately her friend laughs and says, "Oh yes, just adjust the repeats? Let me see..."
She looks at the chart for the pattern and says, "Simple. I'll help you."
I sell the pattern and more yarn to the first knitter.
After they had gone I had a moment to contemplate the experience. I know most people just follow knitting patterns just as they are written. They don't have the confidence to adjust a pattern. They will even knit the sleeves too long because they don't know how to adjust the increasing - or decreasing if you are working top down.
Most of the time it is a matter of basic arithmetic. They could, for the most part, do the arithmetic if you asked them to do a straight forward division or multiplication. Older people would probably do the calculations mentally, younger ones will take out their phones and do it on that. Ask either group to apply the calculation to a problem however and they are lost.
The tension (gauge to readers in North America) is 20sts to 10cms. You want something to measure 100cms? Yes, you need 200sts. You want it to measure 110cms? Yes 220sts. And so it goes on.
I know it is not always easy - and I have given a very simple example - but it can be done.
I was talking to another knitter later in the day. We talked about Philae landing on the comet - something she had, like me, found fascinating. I mentioned how I hoped it might excite current school students to study science, particularly maths and physics. She agreed.
Then she asked me how she could alter the pattern she was interested in. (She's a very big girl and she has to adapt everything to her 1.9m height.)
I told her what she needed to take into consideration but I said, "You teach maths. You can do the calculations yourself."
She looked at me in alarm and I said, "Basic mathematics S...... but send me an e-mail if you aren't happy and I'll check."
"Cheeky Cat!"
Perhaps. It made me wonder though how often I also lack confidence when I am outside my comfort zone.