If you pick somebody else’s trademark and use it to market and sell your products or services, it may be considered trademark infringement.
Trademark infringement is a strict liability offense. What this means is that whether you intended to infringe or not is irrelevant.
For example, if you didn’t know that there was a registered trademark and used it to market your products, hence, you infringed on a registered trademark and you are liable. Also, if you believe your use of somebody else’s trademark is fair use, but it isn’t, you’re liable.
Lesson to learn: always do a proper trademark search before selecting a trademark for use and registration!
To open in a new tab, click: Can I pick somebody else’s registered trademark for use?