Pattern 46: No unpleasant surprises
AKA:

You are trying to ensure the sites has NO MODES (40) and want users to feel safe on your site. You want to provide plenty of FEEDBACK (41).

Reliable behaviour is needed by users. They should be aware of where they are in a progression of actions. They should understand the impact of each action and be sure of its outcome (both on the site and in the world).

Therefore

Use [Next] and [Previous] buttons where appropriate; c.f. BUTTON GRAVITY (77).
Ensure consistency in linked pages by:

• using pop-ups.
• when opening in a new browser window, offset it slightly or display a message saying that you are opening a new window and giving instructions on how to return to the previous context. This is Tidwell’s PILE OF WORKING SURFACES pattern.
• using trapped frames.

Ensure consistency of logins:

• to guarded pages;
• to the home page.

Ensure consistency of navigational links, especially if they are built dynamically. Protect against double form submission. Adopt an attitude of forgiveness: the user is not to blame for errors, its probably your design. Allow them to undo errors. Give feedback on mouse clicks – what is the outcome?

Ensure that the user gets a SENSE OF PROGRESS (48). Consider using BREADCRUMBS (23) and BUTTON GRAVITY (77). TRACK MULTIPLE IDENTICAL REQUESTS (61).

Contributors and sources
Andy Harbach, Jari Worsley

One step forward, one step back, where am I now? Exasperated users will leave your site. We need to exhibit consistent behaviour to build trust. Progress through the site should appear logical and repeatable.

Designed artifacts should be fit for their purpose. They should be natural in behaviour and conform to users’ expectations. There should be no unpleasant surprises except where these are introduced deliberately as alarms. Use of the artifact should give feedback on progress of the task being undertaken. They should fit the mental and manual abilities of users. A very common example of bad interface design outside the context of computers concerns door handles as discussed in Chapter 2.

Forms can mess up predictability (see example below) for several reasons
– session timeouts
– poor server-side code
– poor integration

Example
One bank labels sequential screens with ‘Stage n’ but fails to indicate which stages cause irrevocable commitment to be made. You commit at stage 3 but it doesn’t tell you this until Stage 7.
The present author ordered some beta software from a Microsoft site. After filling in a form he was presented with a ‘parsing error’ screen. Assuming that it didn’t like the phone number beginning +44, he re-entered: with the same result. So he tried again. Two weeks later Microsoft’s fulfiller telephoned, asking: ‘do you really want three copies of this software?’!

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