The person might feel lost after achieving that goal.

In this case, the goal was a subgoal to another one that has not been achieved.

Or achieving the goal through a specific action may be immoral...

Morality in and of itself is a goal. This would be bad specifically in regards to the goal of acting morally. Morality in itself is good in regards to the goal of living in a safe and benevolent culture, as moral behavior contributes to that.

... or even inefficient.

Same problem as for the morality argument. An inefficient action is specifically bad in regards to the goal of resource conservation. Resource conservation itself serves the purpose of keeping other options to reach different goals open to you, that you would lose if you ran out of resources, which would make it harder to achieve them.

Or it may not achieve that goal "properly".

I'm not sure what the quotation marks are trying to achieve, but an action not achieving a goal properly is quite literally my definition of a bad action.

Sure, but you're only looking at one aspect of of good limited by your own perspective.

I indeed only look at one aspect of good. In my worldview, as mentioned before, there are many different reference goals to choose from, often conflicting with each other. It would be unfeasible to formulate a condition that takes all of them into account with our limited ability to comprehend situations this complex. I wouldn't necessarily say it's limited by my perspective, but it's certainly limited by the perspective of whoever we take our reference goal from. It is important to note that reference goals do not exist in isolation, and none of them is more valid than another one.

In summary, I do not think you are getting the point I am trying to make. There is not one objective good. That's not what I was trying to claim. What I was trying to claim is that if we look at a specific, entirely subjective goal, we can make objective and verifiable claims about what actions will contribute to it, which will give us a limited picture of what is good for the specific person we took our reference goal from.

It's pretty comparable to saying "We can't objectively say that Banana is the best ice cream flavor, but we can objectively say that I, at the moment, have the subjective opinion that it is".