An Inside View on a topic involves making predictions based on your understanding of the details of the process. An Outside View involves ignoring these details and using an estimate based on a class of roughly similar previous cases (alternatively, this is called reference class forecasting)
The planning example is discussed in The Planning Fallacy.
Possible limitations and problems with using
outside view are discussed in The Outside View's Domain and "Outside View" as Conversation-Halter . Model Combination and Adjustment discusses the implications of there usually existing multiple different outside views. Taboo "Outside View" argues that the meaning of "Outside View" have expanded too much, and that it should be replaced with more precise terminology.
But I allowed a very different part of my mind, using different considerations, to overrule this judgment; so many extra or missing pieces seemed unlikely. And in the end there was only one missing and no extra pieces. I recall a similar experience when I was learning to program. I would carefully check my program and find no errors, and then when my program wouldn’t run I was tempted to suspect compiler or hardware errors. Of course the problem was almost always my fault.
– Robin Hanson, Beware the Inside View These illustrate failure to use the Outside View. Example 1: Japanese students expected to finish their essays an average of 10 days before deadline. The average completion time was actually 1 day before deadline. When asked when they'd completed similar, previous tasks, the average reply was 1 day before deadline. (Buehler, R., Griffin, D., & Ross, M. 2002. Inside the planning fallacy: The causes and consequences of optimistic time predictions. Heuristics and biases: The psychology of intuitive judgment, 250-270. Cambridge, UK: Cambridge University Press.) Example 2: Students instructed to visualize how, where, and when they would perform their Christmas shopping, expected to finish shopping more than a week before Christmas. A control group asked when they expected their Christmas shopping to be finished, expected it to be done 4 days before Christmas. Both groups finished 3 days before Christmas. (Buehler, R., Griffin, D. and Ross, M. 1995. It's about time: Optimistic predictions in work and love. European Review of Social Psychology, Volume 6, eds. W. Stroebe and M. Hewstone. Chichester: John Wiley & Sons.)
For example, someone working on a project may estimate that they can reasonably get 20% of it done per day, so they will get it done in five days (inside view). Or they might consider that all of their previous projects were completed just before the deadline, so since the deadline for this project is in 30 days, that's when it will get done (outside view).
Another term for taking an outside view
The planning example is discussed in The Planning Fallacy. Possible limitations and problems with using the outside view are discussed in The Outside View's Domain and "Outside View" as Conversation-Halter. Model Combination and Adjustment discusses the implications of there usually existing multiple different outside views.