Many aspiring practitioners of and newcomers to the Vajrayāna come from backgrounds where religion can be studied, practiced, and lived solely through books. This has led to the idea that the same is true for the Vajrayāna, but this is not the case. The Vajrayāna is a tantric vehicle, meaning it follows the tantric framework in study, practice, and progress. Central to the tantras, whether that be Buddhist, Hindu, or Jain, is the master or ācārya. The ācārya is a qualified teacher trained in tantric practices and has the capacity to guide students along the path. For this, we look to the Susiddhikara Sūtra, which states:
Since all mantras are obtained through him, know that an [ā]cārya is the very basis [of all practice].
Mantras, which are central to the Vajrayāna, are not obtained from just anyone or anywhere. They are obtained from an ācārya, and the ācārya is the "very basis" (i.e., foundation, source) of all practice. The same text warns:
[But] if you recite mantras on your own authority without [their having been conferred] by an upādhyāya (preceptor) or ācārya, you will be exerting yourself in vain and will never obtain any result.