I saw someone else do it; Is not a valid reason.
A partner in crime to silent assumption is ‘Accidental pre-conception’.
Assumption can prove harmful to a project and nudge the direction towards a detrimental place.
Accidental pre-conceptions are the Ninja of the self sabotage family. Introduced unknowingly on a wireframe. A rogue button placed without consideration to how it will perform or the effect it may have on the state of other page(s) and items. Stock icons and imagery used as a placeholder, influencing the art direction and colour palette of the application when no prior decisions have been made.
Accidental pre-conceptions require a whole team to be vigilant and to trust each other. Questioning team members work could be taken as an assault on the members ability. Work hard to create an atmosphere in the team where everyone is working to achieve a shared goal. Changing or editing decisions should be a process of the design cycle and achieving that goal.
Frame questions to others in a way as to not assign blame.
”I don’t understand what this button does, can someone explain to me please?”
Imply that you are the one who is ‘behind’ everyone else and need to catch up. When others cannot sufficiently explain to you what the purpose of the query is; giving them space to own the problem in a safe way with room to fix it benefits everyone on the team.
Create time in the day to allow others to explain what they did and why. Not only can you learn from them but if they make a mistake, the act of talking aloud will alert them to this (as the impact of a decision is made real) and they can rectify it avoiding embarrassment.
Encourage designers to share small updates (weekly is best) with teams. Create a feedback loop between the people implementing the design and those crafting the user experience. If the designer hits a problem the weekly sessions work great to fix the problem together, this is in essence, a version of Jikoda. Many minds on a problem all at once may offer a solution far quicker than a lone individual trying to solve the problem on their own.
Teamwork and vigilance are key to staying on top of accidental pre-conceptions and keeping the work free of assumption.