Like my ex employer said I was lacking energy in a job and it wasn't fair on me to keep it going. Also if I had know the full job description I probably wouldn't have applied for it.
"Lacking in energy in a job" - could also mean doing the bare minimum, going through the motions. Show a little more interest in whatever tasks you are asked to do.
Well there you go, he/she obviously believes in you, recognises you have something to give but is disappointed you are not giving the job your best.
Sometimes it is appearances so look smart, be attentive when someone is talking to you, offer to do things before being asked (not all the time though) and generally play your part in the team. You are clearly thought to be capable so be capable.
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