This quote is not in any way properly written English. Regardless, 'for our own good' in any context means to our benefit/our gain.

When the subject is expressed as an excess (eg talks too much, ignores people too often, brushes off achievements too easily etc) then the "for our own good" takes on the negative meaning. He disregards his achievements too often for his own good = he's doing something too much for it to be good for him. He celebrates his achievements for his own good = he's doing something because it's good for him. It's really about how the subject is expressed - if the last sentence above was "He celebrates his achievements too much for his own good", the subject would be that he is something to excess, so "for his own good" would take on the negative connotation.

This is a confusing sentence. Before explaining why, let me show you some good sentences that use "for our own good" with clarity: "We trusted that man too much for our own good." This means we regret having trusted him too much. It would have been better had we not trusted him so much. "We worked too hard for our own good." This means we regret having worked so hard. Now let's look at your sentence. I find it difficult to interpret because I do not know what the speaker might regret. Might he regret following the temptation? Or, might he regret brushing off the achievements? I think he meant to say the former, but he actually says the latter (or, at least, I think he does. In any case, it's not clear.) I think what the speaker meant to say was this: "The temptation to brush off these achievements lightly might be too great for our own good."

to benefit us

In this context, “for our own good” means in a way that harms us, even if we don’t realize it. So the sentence means: We might be too quick to dismiss our achievements, but doing that could actually be bad for us — maybe for our self-esteem, motivation, or mental health. It’s a gentle warning: undervaluing your progress isn’t helpful.