If some unknown person came up to your house and started trying to open each window, jiggling each door handle, and punching in random codes on your garage-door opener, you could safely assume that they sought trouble and that you should stop them. Similarly, if some unknown computer on the internet started probing at ports on your server where you offer no services, it should set off alarm-bells and you should prevent this miscreant from interacting with your server. Especially SSH access. You know what services your machine provides. If anybody attempts to connect to some other service on your machine, in all likelihood they don't have your best interests in mind.
In this post,
to catch inappropriate connection-attempts
and block the offender.