遠慮が無沙汰になってしまいました。
Enryo ga busata ni natte shimaimashita.
For fear of intruding I’m afraid I’ve fallen out of touch.

Now and then you may run into someone —a former colleague, say, or an old classmate—with whom you once had a long-standing tance that has since lapsed. At such times, this polite expression will provide a smooth opening to what could otherwise be an awkward reunion. This sort of greeting will also serve you well if you have occasion to get in touch with a current acquaintance whom you haven’t seen in a long while.

The meaning of the first part of this expression, translated here as “for fear of intruding,” emerges from the key term enryo, the implications of which may be clearer from the following, more elaborate example:

あまりひんぱんにお訪ねしてはご迷惑かと思い、遠慮しておりました。
Amari hinpan ni otazune shite wa gomeiwaku ka to omoi, enryo shite orimashita.
I was afraid I’d make a nuisance of myself by calling on you too often, so I was keeping my distance (out of respect for your privacy).

The use of enryo thus implies that it was neither negligence nor any disinclination on your part that caused you to fall out of touch (gobusata) but only a sense of propriety and respect, lending this handy expression the tone of an explanation (though not necessarily a truthful one) rather than an apology.

In general, such explanations or excuses tend to adhere to a basic pattern: you testify to your original intention to do whatever it was and then point out how fate or circumstances intervened to prevent you from following through. In delivering such an account, you are likely to find one or more of the following expressions useful.

kokoro narazu mo (“in spite of my best intentions”), as in:

心ならずも渋滞に巻き込まれ、到着が三十分も遅れてしまいました。
Kokoro narazu mo jūtai ni makikomare, tōchaku ga san-juppun mo okurete shimaimashita.
In spite of my best intentions I got stuck in traffic and ended up arriving half an hour late.

yamunaku (“be forced”), as in:

病院で検査いたしましたところ安静にせよとのことで、やむなく出発を見合わせました。
Byōin de kensa itashimashita tokoro ansei ni seyo to no koto de, yamunaku shuppatsu o miawasemashita.
I had just had a checkup and they warned me to take it easy, so I was forced to postpone my departure.

It’s not always advisable to lead off with an excuse, however. Suppose you have the bad luck to arrive late for a date—a severely regarded transgression. Your would-be companion is likely to be in a foul enough mood already, and for you to rattle off even a plausible excuse when you finally show up may well have the effect of trying to put out a fire with gasoline. Rather than trying straight-away to justify your lapse in punctuality, it would be much better to lead off with an apology:

ごめんなさい。でも、せめて事情だけでも聞いてくれない？
Gomen nasai. Demo, semete jijō dake de mo kiite kurenai?
I’m sorry. But would you at least let me explain what happened?

Apologies having been made, even if not gleefully accepted, your best chance of salvaging the evening is probably to proceed very slowly—timidly—into an account of how, in spite of your best intentions, you were forced to be late.

– Source: A handbook of common Japanese phrases –