Studies claim that if the user has to wait (e.g., for a page to load) for more than 400ms, then they start becoming disinterested.

This was the outcome of a study from the 1970s, by Walter Doherty and Ahrvind Thadani—so it's possible that in the modern day, people expect software to be even faster.

Churn

• People will churn from slow experiences.
• This happens in a non-linear fashion. i.e., people will tolerate a small amount of latency, but then drop-off fairly rapidly.

Attention & interest

• Slow interfaces (or loading screens) will lower their attention and interest.

Discomfort & frustration

• In some instances, it can actually be uncomfortable to wait. 
• e.g., if you'd just entered your credit card information to buy event tickets, and the interface was slow. You'd be worrying that your tickets had been sold to someone else.

Studies claim that if the user has to wait (e.g., for a page to load) for more than 400ms, then they start becoming disinterested.

This was the outcome of a study from the 1970s, by Walter Doherty and Ahrvind Thadani—so it's possible that in the modern day, people expect software to be even faster.

Churn

• People will churn from slow experiences.
• This happens in a non-linear fashion. i.e., people will tolerate a small amount of latency, but then drop-off fairly rapidly.

Attention & interest

• Slow interfaces (or loading screens) will lower their attention and interest.

Discomfort & frustration

• In some instances, it can actually be uncomfortable to wait. 
• e.g., if you'd just entered your credit card information to buy event tickets, and the interface was slow. You'd be worrying that your tickets had been sold to someone else.