Gmail’s account names (you know, the “left” side of your email address) are very forgiving. Read more for more details!
If you registered your Gmail account name like I did, you likely used the form “firstname.lastname@example.org”. Did you know that it doesn’t matter if you used a period or not! “email@example.com” is treated the same as “firstname.lastname@example.org”. In fact, Gmail is not even case sensitive, so “JohnDoe@gmail.com” is the same as “joHn.doE@gmail.com”! So, not only did you get the email account name you wanted, but you really got more!
Any valid for also works at the login screen too! It surely makes remembering easier!