I'm writing techs right now. Techs (as my client in the USA calls them - more likely to be called specs or specification sheets in the UK), are the instructions to the factory to make the shoe.
So I've prepared my sketch presentation. The clients customer has reviewed it and selected. The collection is ready to be teched and sent to the resource, a week or so ahead of my client who will visit to develop it, there.
So there is this sandal - I spent quite a lot of time on it, my clients customer is very specific about what they like and sent me storyboards of their inspiration to work from.
We all liked this shoe - but I teched it today and half way through my illustrator render, I realised I've designed something that looks great but is physically impossible to construct. Kind of like that building above, by the famous artist MC Escher. Look closer, like I did. Could you build that building? I knew, once I looked closely that no one could build this shoe, and even if you could you would not be able to fasten the straps.
Anyway, I found a solution, the main concern was to not spoil the look of the design. Much swearing and head scratching later, I've done it. I now think it's possible. I had to get a last and cut some strips of paper up and figure it out in 3D but I'm there.
Never underestimate the importance of understanding footwear construction. It's important to create products that can be made, not illusions that remain a fantasy in an artists head.