Let´s say you have decided to make a career change and you are currently trying to find out more about the related job market and how you could succeed in it. A lot of information can be found on the internet, but the most precious advice you can usually get is from people who are already working in the desired field.
If they gave you 15-20 min of their precious time, you might get some useful advice for your next steps and increase your chance in the desired market. But how can you ask someone experienced and busy for something like that?