Please note the distinction between "users" and "threads". There is no real limit on the number of active users for Tomcat unless you implement a Domain that keeps a tally and simply bounces logins after the limit has been reached.
The limit on threads, however, is controlled by server.xml, and that restricts the maximum number of concurrent requests that Tomcat will handle.
Since a web client typically can run several request threads concurrently (this helps in things like loading images), this means that the momentary "concurrent maximum users" limit can potentially be LESS than the
thread limit, even though the long-term number of users may vastly exceed the thread limit.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.