You should not sign a contract unless you are prepared to complete it, even if you encounter unforeseen circumstances. Things happen; people lose their job, die, and get sick. But if you sign a contract, you consent to the possibility of a lawsuit or arbitration to enforce its terms. It is common for people to sign an agreement without reviewing it, or to think they can rescind their acceptance after signing.
If you sign a contract but do not complete it, you may be forced to perform (specific performance). You may be forced to pay the other party the money it spent in relying on your completion of the contract (reliance damages). Or you may be required to pay the other party the amount it would have received if you completed the contract without breaching it (expectation damages).
Expecting people to read the entire terms and conditions of every contract they sign is probably impractical. But every time you sign your name in exchange for something of value, you should consider what the contract requires. If you breach the contract's terms, it is highly unlikely that you can simply walk away.