Consider the following excerpt from the preface of Raja-Yoga by Swami Vivekananda
In the first part some simple and specific directions are given for the student who want to practise, but all such are especially and earnestly reminded that, with few exceptions, Yoga can only be safely learnt by direct contact with a teacher. If these conversations succeed in awakening a desire for further information on the subject, the teacher will not be wanting.
Normal people in my question refers to the people who are not with any special powers or avatar etc., How to understand the above sentence? Is guru mandatory for normal people or one can attempt to do with interest/desire as only necessity?