Moment of Truth
On the face of it, the two jobs aren't that different. The Captain generally isn't working harder than the FO; in many cases, the reverse is true. The Captain is paid more because of the responsibility that comes with being the "final authority" on the operation of the aircraft. In most cases this is a fairly academic point. The FO generally takes part in the decision-making process, and will usually share in any negative outcomes. The FO arrives at the crash scene at the same moment as the Captain; in most cases where the FAA violates the Captain, they violate the FO as well. The reality is that there are about 5 seconds every flight where the Captain really earns the money that comes with the fourth stripe: the moments leading up to V1.
V1 (spoken as "Vee One") is shorthand for takeoff decision speed. It is the moment at which the distance required to continue the takeoff after an engine failure or reject the takeoff and stop the airplane is exactly equal. At speeds less than V1, rejecting the takeoff uses less runway; beyond V1, continuing the takeoff is safer. This speed is calculated for every takeoff and changes with aircraft weight, runway length, and surface conditions (wet runway, snow, etc). Sometimes V1 is the same speed as Vr (rotate speed), but can often be well below Vr, especially in marginal performance situations. In most situations, V1 on the JungleBus is between 130 and 145 knots (150-170 mph).
As the Captain, making the "go/no-go" decision is my responsibility. A high-speed takeoff abort is a very dangerous maneuver that has resulted in quite a few fatalities and injuries, wrecked airplanes, and ruined careers. The decision to abort a takeoff at high speed is not one to be made lightly, but it has to be made within the space of seconds or even fractions of seconds as V1 speed is approached.
For this reason, the Captain has his or her hand on the thrust levers throughout the takeoff roll, regardless of who is flying. At my airline, the Pilot Flying sets takeoff thrust and the Captain takes over the thrust levers. The Pilot Monitoring checks the engine gauges and crew alerting system to make sure all indications are normal; as Captain I keep a good eye on the EICAS even when I'm Pilot Flying. When the airspeed indicator shows 80 knots, the PM calls out "Eighty knots, thrust normal" and the PF responds "Checks." Up to this point, an aborted takeoff isn't a big deal and it's standard to abort for anything out of the ordinary. Beyond 80 knots, however, the risk steadily increases and the critera you'd abort for steadily decrease. As V1 approaches you mentally shed abort items until only an engine failure or loss of directional control remain in the last few seconds before the Pilot Monitoring calls "Vee One" and you take your hand off of the thrust lever, signifying a "Go" decision. Short of the airplane simply refusing to fly, you're going aviating no matter what at this point.
The JungleBus is a bit of a runway hog, and even a 8000 foot runway can be short when you're heavy. Those last few moments before V1 are tense, because you can see the end of the runway rushing towards you as the airplane eats up nearly 250 feet per second. A successful abort with the airplane stopping on the runway looks increasingly improbable. If you did decide a situation merited an abort, you'd command "Abort!" while pulling the thrust levers to idle, then into full reverse. Simultaneously, you'd mash the brake pedals to the floor for maximum braking (the JungleBus has anti-skid). If you do get it stopped before the runway's end, you're not out of the woods yet; your brakes are so hot they're glowing white at this point, and the chance of a fire in the next few minutes is pretty good.
With most of the decisions you make as Captain, you have quite a few resources at your disposal: your FO, flight attendants, dispatcher, manuals, synoptic pages, and maintenance control, to name a few. In most situations you have enough time to gather all the information you need to make a good decision and solicit others' input. Many times the answer is fairly self-evident. In the moments before V1, though, a Captain can be called upon to make the most important decision of his or her career, almost instantaneously and with the very slenderest threads of information to go on. In those moments, the left seat is lonely indeed.