I have encountered a number of people who exhibit startling hostility at being told something they were already aware of. While I cannot currently recall a specific example, I strongly suspect I have previously felt this way myself.
While sharing may be better than assuming when only considering the local optimum, if your signal to noise ratio is bad enough, you will face an impairment to communication that simply wouldn't exist if you had been more selective.
When someone makes a search and lands on your tutorial, you are not giving him unsolicited information.
You would be if it's a tutorial on audio codecs and your tutorial starts with connecting the power cable to the computer, clicking 'log in', and don't forget to breathe!