Imagine a person does not need to campaign to win, they are just adored by 60% of the country (USA) and does not need to do any press. How much work would it take to do all the paper work needed to become president by yourself with no staff?
It is as a practical matter impossible.
While some states allow ballot access by paying a fee or being a nominee of a major political party, others require that petitions with certain numbers of signatures be signed for ballot access. There is no practical way that a Presidential candidate could meet those petition requirements in enough states that require petitions for ballot access without the assistance of at least significant numbers of volunteer supporters to win the required number of electoral votes and to be nominated by a political party if running as a major or minor political party candidate.
If the Presidential candidate runs under the banner of a major political party, the candidate also has to supply and approve delegates for the national convention and delegates in connection with state caucus processes. The petition requirements for general election ballot access are much more onerous for independent and minor party candidates than they are for major party candidates.
A Presidential candidate also has to name several hundred volunteers to serve as Presidential electors for his or her campaign, cannot carry out this step personally, and must authorize the proposed electors to serve on his or her behalf.
It is theoretically possible to do all of this without paid staff or paid advertisements, but it is not possible to do this without significant numbers of volunteers if one doesn't have paid staff to do it.
CAVEAT: There are a couple of back door possibilities that could avoid this necessity, even though they aren't strictly in the spirit of the question.
A major political party candidate could pick our candidate to be his or her VP nominee, while our candidate simply agrees to serve as VP and does nothing. Our candidate's ticket wins the election. The electoral vote is held confirming that our candidate's ticket wins. The top of the ticket Presidential candidate then dies before being sworn in. Our candidate becomes President.
Both the Presidential and Vice Presidential nominees whose electors win a majority of the electoral vote on election day die before the electoral college vote is held. The electors of the various state confer with each other about who to nominate in lieu of their pledged candidates on the day of the electoral college vote and they vote in favor of our candidate, due to our candidate's wide popularity, quickly reaching a consensus in favor of this candidate. Our candidate wins the electoral vote and becomes President.
In the scenarios above, deaths could be replaced with voluntary resignations from campaigning at the relevant junctures (the classic reasons is "to spend more time with family").