Remember those insane graphical puzzles from the 80's where you had drawings of thousands of people all crammed together in a forest or something and you had to find "Waldo" in there somewhere? Well that's how I feel sometimes trying to find a tool in my shop.
Don't get me wrong, I am actually a very organized person and I always try to follow the first rule of being organized: A place for everything ...". And right after I clean my shop, everything is in its place and I know just where to go for whatever it is that I need at that moment.
But then I start working on a project and I just know I'm going to need that pencil or ruler or hammer or chisel again in just a sec so I end up breaking the second rule of organization: "Don't put it down, put it away". I mean really, am I going to walk across the shop to put a tool back "where it goes" when I'm going to need it again in five seconds? Of course not. Make this call a few times and pretty soon your tools are scattered all over the shop again.
Some guys try to deal with this problem by wearing tool belts or building tool carts that can be moved around the shop. But Murphy's Law states that the tool you need will always be as far away from you as it can be. It does not matter how many tools you pack around with you. Murphy's Law is very clear on this. Regarding tape measures, rulers, pencils and or putty knives, it does not matter how many you own or how many you scatter around your shop. There will simply never be one within reach. Tool belts and tapes with belt clips may seem like a good way to circumvent the inevitable. But sooner or later you will end up catching the thing on something and ripping your pants off. And, again, according to Murphy's Law, it will be when you have a customer standing right next to you.
I have actually spent a notable amount of time, over the years I have been a woodworker, wandering around my shop looking for a tool I had in my hand the whole time. I did not have to "get older" to experience this phenomenon. I was just as capable of doing this when I was 20 as I am now that I'm 60. It seems that this is just a part of shop work we have to accept. In extreme cases, it might even need to be factored into your bids ...