The reason that planning software development is bullshit is that you simply cannot know all the little details because in software development you're always doing something you've never done before (because if you did you could just copy-paste your previous work). To use the 'going to the supermarket for milk' example. I could make a fairly accurate estimate for that because I've gone to the supermarket hundreds of…
- how long will research take? Where do you buy milk? Where is the nearest shop? 3 mins.
- how long to get to nearest shop and back (eg 10mins x 2) = 20 mins.
- find milk in shop (30 secs to 5 minutes), so say 4 mins.
- Buy milk. (1 to 5) say 3 mins.
Don't forget that these are estimates and always add a bit of headroom. The above comes to 31 mins, so say 35 and you know you're covered. If the manager isn't happy with it, give him the low down figures.