Is it possible to hack any system with metasploit only?

In general hackers or crackers aim to install their own payload on the compromised machine. With Metasploit you can do that without having any networking or security knowledge. Simply run a few commands and you will be cracking into remote machines. My friends used it to create APKs that were distributed over file sharing websites. People are so stupid that they download anything that's labelled FREE. Once the user has downloaded the APK you can literally own their phone. I won't go into details; but I know it works because I saw it with my eyes. 

Just a word of caution though. Be careful to not cause any damage to the client machine. The bigger problem is dealing with police who won't understand the difference between cracking and safe-hacking. 

I wouldn't say that you can hack into any system with metasploit. But what you can get is atleast a basic connection with the target through vulnerabilities present in the machine. Metasploit can get you a shell in quick time if you have all detailed report about the target system. 

Now what is hard part in Metasploit is getting your payload to the target successfully. There are numerous ways to do that.

But just using metasploit you cannot do any miracle. If you have all info about your target then Metasploit makes thing easy for you.