Thoughtlessly is the adverb from 'thoughtless' — it describes HOW something was done: without stopping to think about the people it would touch. 'He thoughtlessly parked across the driveway.' 'She thoughtlessly repeated what I had told her in private.' Because it goes with the verb, it quietly does something kind: it blames the action rather than the person. Compare 'He is thoughtless' (that is who he is) with 'He acted thoughtlessly' (that is what he did this once). English speakers reach for the adverb when they want to complain about the behaviour and leave the person's character alone — a useful move in an office, and worth teaching as a skill, not just a word. It also carries the lighter sense: done automatically, without attention. 'She thoughtlessly dropped the receipt in the bin' — no unkindness, just no thinking. Position: usually right before the verb ('he thoughtlessly said…'), or at the end ('he said it thoughtlessly'). It is a slightly formal, written-feeling word. In speech, most people would say 'without thinking' instead — 'He said it without thinking' is the everyday version and sounds more natural in conversation.

不體貼地、沒替別人著想地；也可以是「沒多想就（做了）」。口語其實更常講 without thinking。