How would you interact with an employee who is always a failure in his career and assigned jobs, as a HR Manager?

Retain your employee and give him proper training, when Hr conduct the performance evaluation, check on which part the employee is failing to perform and give the employee necessary training and orientation. 

There's a limit to which one can continue with a person who fails too often. But a person who fails in a particular role may be roaring success in another role. I always prefer to set people up for success. Therefore, I'd say we explore the options - whether we can re-train / transfer to a more suitable area / etc, and hope he makes a success of himself.

One cannot be tolerating constant failures, and such people are bound to be eased out by any system.

Try not to remove the employee rather give him chance to fit in a suitable field. i think this way because the company might have spent alot on this particular employee

Their work

I will start the interaction with finding out his/her problems/.issues and give counseling to over come the problems. I'll give the employee a time limit to change his working style and performance. Most of the cases they'll change if the problems are genuinely addressed Still if  there is no improvement, I'll suggest not to retain.  

As an HR Manager you and your department must exhaust all possible means to retain your work force. A periodic or scheduled evaluation and assement of employees vs. respective JD follow thru with necessary training would go a long way also counseling oe employee relation JD

Proper table talk discussion and right orientation can help a lot.