Most young people, at some point in their education about music, learn about the harmonic trick of Tristan. What a discovery! They’ll look at you and discourse about how Wagner refused to resolve to the tonic until the very end of the opera, about how he used that device to sustain a high level of emotional tension until the very end, maybe even about how the whole harmonic structure, with its resolution at the end, is really meant to mimic something about the birds and the bees. (Every generation seems to believe that it discovered sex and Tristan.)
It’s a big discovery for young people and of course, everything they are telling you about Tristan’steasing harmonic strategy is proven, quantifiable by harmonic analysis, and true. It’s not true, however, that Wagner was the first composer to pull this card out of the deck of harmonic tricks. Here are a few of my favorite examples of composers who, long before Tristan, were stalling about resolving onto the tonic. (Please note that I will refer to timings in the videos below rather than bar lines. Heck, you might not have scores on hand . . .)
Beethoven Symphony no. 6 in F Major, op. 68 (“Pastoral”), first movement
Beethoven’s programmatic title for this movement is “Erwachen heiterer Empfindungen bei der Ankunft auf dem Lande,” a mouthful that can be translated as “the awakening of happy emotions upon the arrival in the country.” He sustains that mood of ineffable happiness by refusing to fully resolve back to the tonic key of F Major for a long time. In this performance of the Vienna Philharmonic conducted by an uncharacteristically calm Leonard Bernstein, that moment doesn’t come until about 2:44 into the video.
So you see, Beethoven could string us along nearly as effectively as Wagner could, just by teasing us until he resolves back to the tonic.

Mendelssohn Violin Concerto in E minor, op. second movement

Got to admit it – this is about my favorite example of a composer’s ability to sustain emotional tension by refusing to resolve back to the tonic. You can call the mood that Mendelssohn creates here anything you want – longing, love, it’s your call. Whatever it is, it really works in this movement.
In this wonderful 2006 performance by Itzhak Perlman, that resolution back to the tonic doesn’t come until about 3:30. That’s a long time to wait, but well worth it. (Remember, you theorists, that this second movement is in C Major, not the E minor of the first movement.)

Bellini, Norma, final scene
If you listen to the last three minutes or so of Bellini’s opera Norma, which was written decades before Tristan, you’ll notice that Bellini (a genius who died much too young) teases us and then lands solidly back on the tonic of F Major not once, but twice. But then he really nails it hard. I really wonder whether there could have been a Tristan if there had never been a Norma.  I don’t know – what do you think?
Here’s a video of the last five minutes of Norma, featuring American soprano Brenda Harris. Pay special attention to the last two minutes and hear those big crash landings back into the tonic at about 3:50 and again about a minute later.