There are lots of bugs in peoples' brains that prevent them from doing things that seem like good ideas, and I don't think the fear of becoming illegible (
http://www.ribbonfarm.com/2011/07/31/on-being-an-illegible-p...) is anywhere near the most important one.
My vote for the most important bug is as follows.
It looks as though human brains were architected to think in two modes: "near" mode and "far" mode. The reason for this is that early human tribes had important rules that directly impacted survival and reproduction (for example, "don't take more than your share of the food", "don't sleep with another man's wife"). It was critical for us to tell others that we were going to uphold these rules or we would get kicked out of the tribe. At the same, time our genetic fitness would increase massively if we could find a way to covertly break those rules while still upholding them verbally (more food and more descendents for successful rule breakers).
The upshot of this is that even if something looks good when processed using far mode it's not necessarily easy to translate it into near mode where it actually gets done.
In my view, this is an explanatory factor for procrastination as well. For example, the popular Google Chrome extension Chrome Nanny (https://chrome.google.com/webstore/detail/gpdgmmdbbbchchonpf...) requires the user to enter 64 random alphanumeric characters before visiting a distracting site--which moves the idea of visiting this site from near mode (where it might actually happen) to far mode (where it won't).
For more on near and far modes you can read http://www.overcomingbias.com/2010/06/near-far-summary.html. Note that novel tasks and desirable risky acts are both associated with far mode.