I'm somewhat guilty of this when someone is asking me to do something for them whether it's work-related or personal. But, it's only when someone is approaching me out of the blue with some request.
I like helping other people. I just don't want to let them down because I forgot about it because I was caught in between. I tend to use my email/voicemail/texts as a "to-do" list. I see it and I remember.
If I'm asking someone else for something (their time, knowledge, expertise, opinion...), the onus is on me. I plan it. "I'd like to talk to you about xyz, when would be a good time?" (Yes. I can be really anal and annoying. However, when I want to accomplish something, it usually turns out according to plan).
At work, I'm only supposed to be working on one project at a time, but it doesn't work that way. People need things and they ask. I want to find the time to accommodate them, but can't always fit it in right then. "You want something from me? This is what I need. Email me or I'll forget". This happened to me today. I was in the middle of taking some annual compliance training online and was interrupted by someone looking for information. I was more than happy to help them, but the timing wasn't good. So, I committed the sin. I told them to ask me tomorrow or send me an email to remind me. Right then, I needed to finish that training and get my boss off my butt.
Personally, I work a long day and have over an hour of commute time each way. Most of my communication is done in the car, on my bluetooth. I love my family and friends, but if I'm driving and you tell me that you need something from me, you'd better follow it up with an email/voicemail/text or I may not remember it by the time I get home.
If you're asking me, be willing to accommodate my request of a reminder email/voicemail/text.
If I'm asking you, you tell me the terms. (If you don't, I may very well ask you to email/voicemail/text me).
Sorry for the long response.