Agreements and authorship
Authorship gets negotiated. Ownership of data, materials and code usually gets discussed only once something valuable exists — which is the worst moment for it.
Working across cultures
If your partner has never pushed back on anything, that is not agreement. It usually means the objection was raised in a register you are not reading.
International funding
Most grant negotiations settle salaries and travel. The line that quietly breaks a partner's budget is the one covering everything not attached to an activity.
Co-writing and publishing
A disagreement about where to submit is rarely a disagreement about quality. It is usually two evaluation systems pulling two people in different directions.