Two tickets means no protection.

Because it decides who absorbs the failure. On a single ticket a missed connection is the airline's problem — they rebook you at no cost, because the itinerary was sold as one journey. On separate tickets the second carrier owes you nothing, and the replacement is a walk-up fare bought on the day, which is usually the most expensive way to buy a seat. Changing to an earlier first flight is almost always cheaper than the failure it prevents.

Almost none of it is walking. Gate closure takes fifteen to thirty minutes off before anything else — your deadline was never the departure time. Deplaning from a rear seat on a large aircraft can take twenty minutes before you've moved anywhere. Then terminal transit, security re-screening if applicable, and baggage reclaim and re-check if the bags don't go through. Immigration, where it applies, is the largest and least predictable block of all.

Ask the airline for your specific itinerary, because it differs by airport and route rather than following a general rule. Many international-to-international connections stay airside with no border crossing; others require entering the country formally even in transit. And in some countries an international arrival means clearing immigration and customs and re-checking bags before any onward flight, including a domestic one. If you can't verify it confidently, assume it applies.

A seat near the front is the most reliable purchasable minutes there are, and cabin baggage only removes reclaim and re-check entirely. The free parts: look up both gates before you land, and tell the cabin crew before descent that you have a tight connection — they can sometimes ask other passengers to let connecting travellers off first, and it works more often than people expect. Stopping to buy anything is the most common self-inflicted loss.

On one ticket, go to the airline's transfer or connections desk rather than joining a check-in queue, and ask about the next available flight on any carrier rather than only theirs. On separate tickets the second airline is under no obligation, though some offer a reduced change fee as goodwill if asked politely — worth trying, not worth planning around. And check your insurance: missed-connection cover frequently requires a minimum connection time to have been booked, which excludes exactly the tight ones people worry about.