If you read and actually considered the worst case in every contract/website terms and conditions/software licence that you come across it would probably take a

If you read and actually considered the worst case in every contract/website terms and conditions/software licence that you come across it would probably take about a day a week and you would never actually agree to anything that wasn't a GPL/BSD/MIT... software licence. For one thing most give the party offering the agreement rights to change it which should be an absolute no-way. For most things such as online purchases I tend to rely on law and reasonableness of people and take the chance without reading expecting the maximum downside to be tens of pounds related to that purchase. I am a little more careful when locked into eco-systems (Kindle/app-stores) but still go a fair bit on taking the risk with the reputation of the provider and the size of the risk and the cost of getting the content another way.